There is known a drive system including a first electric motor, a first gear device, a second electric motor and a second gear device. Patent Documents 1-3 disclose such a drive system for a hybrid vehicle. For example, the drive system disclosed in Patent Document 1 includes, as the first gear device, a planetary gear device functioning as a power distributing mechanism. The planetary gear set is configured to distribute a drive force produced by an engine to the first electric motor and the second gear device. The second gear device includes a planetary gear device functioning as a speed reducing mechanism to reduce the speed of a rotary motion and transmit the rotary motion to drive wheels. The first electric motor functions primarily as an electric generator, while the second electric motor functions primarily as an electric motor used as a drive power source in addition to the engine, to produce an assisting drive force for driving the drive wheels.
In the drive system of Patent Document 1, the casing structure consists of a first casing, a second casing and a third casing. The first casing accommodates the first electric motor and the first gear device, and the second casing accommodates the second electric motor, while the third casing accommodates the second gear device. In assembling the drive system thus constructed, a first unit is prepared by accommodating the first electric motor and the first gear device in the first casing, a second unit is prepared by accommodating the second electric motor in the second casing, and a third unit is prepared by accommodating the second gear device in the third casing. The first, second and third units are then assembled together such that the first and third units are disposed on the respective opposite sides of the second unit,
Patent Document 1: JP-2003-191759 A
Patent Document 2: JP-2003-191761 A
Patent Document 3: JP-2003-336725 A
The drive system of Patent Document 1 manufactured by assembling the three separate units such that the first and third units are disposed on the opposite sides of the intermediate second unit suffers from a problem of a low efficiency of assembling due to a relatively large number of structural divisions of the drive system.
A first aspect of this invention was made in view of the background art described above. It is therefore an object of the invention to provide a vehicular drive system which has an improved efficiency of assembling.
The vehicular drive system disclosed in Patent Document 1 includes an output shaft, and bearings for rotatably supporting the output shaft. The drive system of Patent Document 1, which is a drive system for a hybrid vehicle, includes the first electric motor, the planetary gear device functioning as the power distributing mechanism for distributing the output of the engine to the first electric motor and the output shaft, the second electric motor connected to an output shaft of the power distributing mechanism, and the planetary gear device which connects a rotor support shaft of the second electric motor and the output shaft of the drive system. The output shaft of the drive system is rotatably supported by the casing via the bearings.
The drive system installed on the vehicle is preferably made as light as possible. On the other hand, support members such as the bearings for supporting the output shaft must be lubricated with a lubricating oil. The lubricating oil supplied to the support member must be discharged through a suitable discharging oil passage system. The provision of an exclusive member to provide the discharging oil passage system is contrary to the above-indicated need for reducing the weight of the drive system. Even if the discharging oil passage system is formed without the provision of the exclusive member, the need for minimizing the weight of the drive system still exists.
A second aspect of this invention was made in view of the background art described above. It is therefore an object of the present invention to provide a vehicular drive system which is constructed to have a reduced weight.
There is also known a vehicular drive system including a differential mechanism in the form of a planetary gear set for distributing an output of a drive power source such as an engine to an electric motor and a power transmitting member. The hybrid vehicle drive systems disclosed in Patent Documents 1 and 4 are examples of this vehicular drive system. In the hybrid vehicle drive system disclosed in Patent Document 1, one of three rotary elements of the planetary gear set is connected to the electric motor, and another of the rotary elements is connected to the drive power source, while the other rotary element is connected to the power transmitting member. The rotating speed of the power transmitting member is continuously variable by controlling an electric load acting on the electric motor. Accordingly, the vehicle can be run with the engine kept in its optimum operating state, so that the fuel economy of the vehicle is improved. The fuel economy can be further improved where a second electric motor is provided in addition to the electric motor connected to the differential mechanism, such that the second electric motor is disposed between the power transmitting member and the drive wheels, so that the second electric motor is operated by an electric power generated by the electric motor connected to the differential mechanism, to drive the drive wheels.
Patent Document 4: JP-3454036
In the vehicular drive system described just above, the rotating speed of the power transmitting member is controlled by controlling an electric reaction force of the electric motor connected to the differential mechanism. In this drive system, therefore, the size of the electric motor must be increased with an increase of the output capacity of the engine, and the required overall size of the vehicular drive system undesirably increases with the increase of the size of the electric motor.
In view of the problem indicated above, it is considered, for example, to provide a coupling device or a differential limiting device connected to the planetary gear set functioning as the differential mechanism, so that the planetary gear set is selectively placed in a non-differential state (namely, in a locked state). The planetary gear set is placed in the locked state by the differential limiting device when the engine is operating in a high-output range, to reduce the maximum value of the electric reaction force generated by the electric motor, whereby the required size of the electric motor can be reduced.
Where the differential limiting device described above is provided, however, the differential limiting device must be connected at a portion thereof to the sun gear of the planetary gear set. Where the differential limiting device and the sun gear are splined to each other, there is a risk of a low degree of accuracy of radial relative positioning of the differential limiting device and the sun gear.
A third aspect of this invention was made in view of the background art described above. It is therefore an object of the invention to provide a vehicular drive system wherein the differential limiting device provided for the differential mechanism has a high degree of support accuracy.
Hybrid vehicle drive systems disclosed in Patent Documents 2, 5 and 6 are known as a vehicular drive system including a differential mechanism for distributing an output of a drive power source such as an engine to an electric motor and a power transmitting member. In the drive system disclosed in Patent Document 2, for example, a planetary gear set functioning as the differential mechanism, a first input shaft receiving the output of the drive power source, and a second input shaft (intermediate shaft) receiving an output of the first input shaft through the planetary gear set are disposed coaxially with each other, such that the sun gear of the planetary gear set and the rotor of the electric motor are rotatable as a unit, and the ring gear of the planetary gear set is connected to the second input shaft through a power transmitting member in the form of a flange formed at one end of the second input shaft, while the carrier of the planetary gear set is connected to the first input shaft such that the carrier and the first input shaft are rotatable as a unit.
In the drive system described just above, the rotating speed of the power transmitting member is continuously variable by controlling an electric load acting on the electric motor, so that the vehicle can be run with the engine kept in its optimum operating state, whereby the fuel economy of the vehicle is improved.
Patent Document 5: JP-2004-161 A
Patent Document 6: JP-2000-85387 A
In the drive system disclosed in Patent Document 2, the first and second input shafts are required to have a high degree of accuracy of coaxial relative positioning. In this drive system of Patent Document 2, however, the first input shaft is supported by the rotor of the electric motor, so that the axial length of support of the first input shaft by the rotor is limited to the length of the rotor. Where the rotor has a relatively short length, therefore, the accuracy of support of the first input shaft by the rotor tends to be low, and there is a risk of a low degree of accuracy of coaxial relative positioning of the first and second input shafts.
A fourth aspect of this invention was made in view of the background art described above. It is therefore an object of the invention to provide a vehicular drive system wherein an input shaft receiving the output of a drive power source is supported with a high degree of accuracy.